Stabilization of cholesteric-phase liquid crystal compositions against true solid formation,using cholesteryl p-nonylphenyl carbonate

ABSTRACT

STABILITY OF CHOLESTERIC-PHASE LIQUID-CRYSTAL COMPOSITIONS IS IMPROVED BY INCORPORATING THEREIN CHOLESTERYL PNONYLPHENYL CARBONATE, A NEW COMPOUND, MADE BY REACTION OF CHOLESTERYL CHLOROFORMATE WITH P-NONYLPHENOL AND PYRIDINE. THE P-NONYLPHENYL CARBONATE DOES NOT CRYSTALLIZE TO TRUE SOLID IN THREE YEARS, BUT THE CORRESPONDING P-OCTYLPHENYL CARBONATE STARTS CRYSTALLIZING TO TRUE SOLID IN THREE WEEKS.

Patented May 25, 1971 ABSTRACT OF THE DISCLOSURE Stability of cholesteric-phase liquid-crystal compositions is improved by incorporating therein cholesteryl pnonylphenyl carbonate, a new compound, made by reaction of cholesteryl chloroformate with p-nonylphenol and pyridine. The p-nonylphenyl carbonate does not crystallize to true solid in three years, but the corresponding p-octylphenyl carbonate starts crystallizing to true solid in three weeks.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to a novel chemical compound, cholesteryl p-nonylphenyl carbonate, to the use thereof as a stabilizer in cholesteric-phase liquid-crystal compositions, to the stabilized compositions, and to articles made from them.

(2) Description of the prior art Liquid-crystal materials have long been known (F. Reinitzer, Wiener Monatschr. Chemi 9, 421 (1888)). They behave mechanically like liquids (exhibit flow) and optical-1y like crystalline solids (exhibit berefringence). Liquid-crystal materials may be classified as cholesteric, nematic, or smectic. Many of the cholesteric-phase liquidcrystal materials exhibit selective scattering, i.e., they change apparent color upon slight changes in temperature within a color-play temperature range that may range over about 10 C. or more, e.g., red at 1-6 C. and violet at 26 C., with the other colors of the visible spectrum in between, or may be as narrow as 1 C., e.g., red at 94 C. and violet at 95 C. Such compositions may conveniently be produced as films by dissolving the appropriate compound or compounds in suitable organic solvent (benzene or petroleum ether may be used) and pouring the solution onto a surface to permit the solvent to evaporate, leaving a film perhaps 1 to 50 microns thick. The film is then used for temperature mapping (tumors can be detected in this .way) or for other purposes.

One difiiculty with cholesteric-phase liquid-crystal materials that have a relatively high color-play temperature range, prior to the present invention, has been that they tend to be unstable, crysta-llizing into a true solid. This may happen in several hours, or it maye take a few weeks, but before this invention, a composition of this kind that would remain liquid for years was unknown.

The production of cholesteryl carbonates is well known to persons versed in the field of cholesteric-phase liquid crystals. Cholesteryl chloroformate, either as a reagent or made in situ by the action of phosgene upon cholesterol, is reacted with pyridine and an alcohol or a phenol, the reaction being driven by the formation of pyridine hydrochloride, which is insoluble in the reaction mixture. The reaction mixture is filtered, and the carbonate is then isolated from the filtrate.

BRIEF SUMMARY OF THE INVENTION Stability of cholesteric-phase liquid-crystal compositions is improved by incorporating therein an effective amount of cholesteryl p-nonylphenyl carbonate, a new compound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Making cholesteryl p-nonylphenyl carbonate cholesteryl chloroformate, either as a reagent or formed in situ by reacting phosgene with cholesterol, is reacted with pyridine and p-nonylphenol, with pyridine hydrochloride being precipitated and removed by filtration. The carbonate is then isolated from the filtrate. The chief chemical reaction involved is that of the following equation:

GEH11 CH3 nHm R My CO I N 01 I Pyridine OH cholesteryl chloroformate p-nonylphenol 8 CH3 I Oholesteryl p-nonylphenyl carbonate Pyridine hydrochloride A three-necked glass flask having standard-taper ground-glass joints is fitted with a reflux condenser, a stirrer, and an additional funnel. The flask is charged with 1 gram-mol of cholesteryl chloroformate (449.2 grams) dissolved in 800 milliliters of benzene. Through the addition funnel, there is slowly added with constant stirring a mixture of 1 gram-mol (220 grams) p-nonylphenol, 1 grain-mol (79.1 grams) pyridine, and 600 milliliters of benzene. After the addition is complete, the flask is heated to and maintained at reflux temperature for 1.0 hour. The reaction mixture is then cooled to room temperature. During the addition and the subsequent heating, there is formed by the reaction of the equation cited above a solid, namely, pyridine hydrochloride, and it is removed from the reaction mixture by vacuum filtration. The filtrate comprises a benzene solution of the desired cholesteryl p-nonylphenyl carbonate, and the benzene may be removed from this solution with the use of heat and vacuum techniques to obtain, in good yield (about %98%) the desired carbonate, a very viscous paleyellow liquid.

It should be understood that chloroformates of other B-hydroxysterals, (other than cholesterol) may be substituted for the cholesteryl chloroformate of Example 1. For example stigmasteryl chloroformate may be substituted for the cholesteryl chloroformate.

Using cholesteryl p-nonylphenyl'carbonate The novel carbonate is used by incorporating it in cholesteric-phase liquid-crystal compositions. It may be mixed readily with any of a great number of compounds 4 In the above examples, the procedure was the same as for the examples of Table 1, except that the color response to temperature changes Was noted by determining the temperatures at which green was observed, thereby locating the approximate of the full color-play temperature l' u'd c stals it iel figiifitfiis253$;fiti i fififattct nIZy be 5 In a t e was made a ee shad to British Pat N 1 041 490, lines 5 102 of page 4, iron that did not, within one year, exhibit any true-solid tion. for a comprehensive (but by no means complete) list of erma compounds suitable for use in making such compositions. t Alfihleugh i e and t i The novel carbonate is effective when used in amounts 0 e e e estery. p'nenyp eny eel E n It IS to exas small as about 5 Weight percent of the stabilized come e that In some F t P i will be pesslble to position and it may be used in greater amounts up to obtain results substantially similar with other compounds about percent by Weight, though in most -instances closely related 1n structure 311?}31'013611168. For example, there is no particular reason for using more than about the double 9 at the se'pesmen of eholesterel may be 20%. The novel carbonate itself does not change color, Saturated Wlth hydrogen end/Or halogen to yleld m" and stabilized compositions containing great amounts of g e er g g and eegrespendlgg the carbonate accordingly are less vivid in their changes ear i i t z fi of color than compositions stabilized with less of the novel expee e 0 ex 1 1 sum i S a 1 lzmg e ee 9 1t carbonate has been found, as mentioned above, that the ad acent Peculiarly, the novel carbonate is far more effective homeleg cholesteryl. P'eetylphenyl carbonate does not as a stabilizer against formation of true solid than its have j Stablhzmg effect of the nenylphenyl adjacent homolog, cholesteryl p-octylphenyl carbonate. benete It likely that theeeeylphenyi earbonate and The octylphenyl carbonate begins to crystallize to a true undeeylphenyl carbonate exhlblt effects Sunder v f of solid upon standing for three Weeks, but the novel carbonr the novel nonylphenyl carbonate but such P P? ate Shows no Signs f undergoing Such crystallization have not been prepared because of the unavailability of upon standing for a period of three years. the corresponding alkylphenols. Results substantially sim- The following table presents specific examples that i131 y 9 be expected with methyl other lower illustrate the use of the novel carbonate in cholestericalkyl defivatlves of cholesterol Cholestaflolphase liquid-crystal compositions: The effects and advantages of the invention, especially TABLEI Oholesteryl cholesteryl Colorp-nonylcholesteryl Cholesteryl p-n-butoxyplay phenyl 2,4-di- 3,4-dichloro- Cholcsteryl phenyl temp. carbonate benzoate benzoate nonanoate carbonate rang Example (percent) (percent) (percent) (percent) (percent) C.)

Cholesteryl 2,4-dichlorobenzoate melts at 128.5 C.- 129.5 C. and clears at 202 C. Cholesteryl 3,4-dichloro benzoate melts at 150 C.-l57 C. and clears at 185 C. Cholcsteryl nonanoate melts at 793 C.-80.0 C. and clears at 1.8 C. Cholesteryl p-n-butoxyphenyl carbonate melts at 113 C.l15 C. and clears at 160 C.

The above compositions are made in the usual manner, namely, by mixing the named components in the amounts indicated with a suitable solvent, such as benzene or petroleum ether, and then forming a film by pouring the mixture onto a surface to permit the solvent to evaporate therefrom, leaving a stratum about 1-50 microns thick. The compositions may also be encapsulated in plastic capsules and the stratum may be formed from the capsules.

None of the compositions in the above table exhibited any true-solid formation within a year, but control com- CH3 R3 where the linkage positions, otherwise the same but with the novel carbonate omitted, exhibited true-solid formation Within several B hours to several days. is selected from the group consisting of Additional examples are presented in Table II, from 1 C 0 Which 1t Wlll appear that additlons of cholesteryl crotonate or cholesteryl benzoate Will lower and broaden the color- CHX play temperature range. Percentages are by weight. H

TABLE II Cholesteryl p-nonyl- Temp. phenyl Cholesteryl cholesteryl Cholesteryl cholesteryl for carbonate crotonate nonanoate benzoate chloride green Example (percent) (percent) (percent) (percent) (percent) 0.)

and

X being a halogen, R is a saturated aliphatic alkyl radical containing 9* to 11 carbon atoms, and R is selected from the group consisting of hydrogen and alkyl and alkenyl radicals containing 1 to 10 carbon atoms.

Thus, it is apparent that the invention aifords a new class of stabilized cholesteric-phase liquid-crystal composition that, like the known compositions, will find use in such applications as thermal-pattern-sensing devices, devices for sensing rate of shear, and the like.

While I have shown and described herein certain embodiments of my invention, I intend to cover as well any change or modification therein that may be made without departing from its spirit and scope.

I claim as my invention:

1. A composition of matter for use in stabilizing cholesteric-phase liquid-crystal compositions against truesolid formation comprising a compound having the formula CH3 R: CH3

where the linkage is selected from the group consisting of X being a halogen, R is a saturated aliphatic alkyl radical containing 9 to 11 carbon atoms, and R is selected from the group consisting of hydrogen and alkyl and alkenyl radicals containing 1 to 10 carbon atoms.

2. A composition as defined in claim 1, characterized in that said compound is cholesteryl para-nonylphenyl carbonate.

3. A method of stabilizing liquid-crystal compositions against true-solid formation, said method being characterized by the step of incorporation in said composition an effective amount of a compound having the formula CH3 R2 CH3(\ n R C0 where the linkage is selected from the group consisting of C H CHX CHa CH1;

where the linkage is selected from the group consisting of X being a halogen, R is a saturated aliphatic alkyl radical containing 9 to 11 carbon atoms, and R is selected from the group consisting of hydrogen, alkyl and alkenyl radicals containing 1 to 10 carbon atoms.

6. A material as defined in claim 5, characterized in that said compound is cholesteryl para-nonylphenyl carbonate.

7. A stratum about 1 to 50 microns thick of a liquid-- crystal containing 5 to weight percent of a compound having the formula where the linkage is selected from the group consisting of 8. A stratum as defined in claim 7, characterized in 5 that said compound is cholesteryl para-nonylphenyl carbonate.

9. A stratum as defined in claim 7,'characterized in that said liquid-crystal material is in capsule form.

10. A stratum as defined in claim 8, characterized in 10 that said liquid-crystal material is in capsule form.

Referen es Cited UNITED STATES PATENTS 3,114,836 12/1963 Fergason et a1. 250-83 3,409,404 11/1968 Fergason 252--408 JOHN T. GOOLKASIAN, Primary Examiner M. E. MCCAMISH, Assistant Examiner US. Cl. X.R. 

